Impulse actuated lock-in switch



T. H. LONG IMPULSE ACTUATED LOCK-IN SWITCH Filed Feb. 23, 1953 flnode Cafhode Pofenf/a/ INVENTOR 7720/7705 H. Long ATTORNEY Aug. 28, 1934.

WITNESSES;

patented Aug. 28, 1934;

UNITED STATES LS'ZLSZZi PATENT GFFEQE HWPULSE ACTUATED LOCK-IN SWITCH vania Application February 23, 1933, Serial No. 658,042

14 Claims.

My invention relates to lock-in relays and has particular relation to impulse actuated lock-in relays of the type incorporating electric discharge devices. 7

It is an object of my invention to provide a lockin relay of simple andinexpensive structure.

Another object of my invention is to provide a relay that shall be capable of actuation in either sense and when so actuated, shall lock itself in in a manner predetermined by the sense of the actuation.

Still another object of my invention is to provide a reversible lock-in device that shall be capable of responding to signals of short duration and locking-in in response thereto.

A further object of my invention is to providev a power amplifying relay, the amplification factor of which shall be capable of abrupt variation by an impulse of predetermined magnitude, that after receiving such an impulse, shall be stabilized in a region of amplification different from the region in which it originally operated and that shall be incapable of preceptable variation from this region by reason of actuations by impulses having a magnitude smaller than a predetermined value.

An incidental object of my invention is to provide a relay of the type incorporating an electric discharge device having a control electrode and a plurality of principal electrodes wherein the power output of said electric discharge device shall be capable of abrupt variations from one region of values to another region of values by reason of potential impulses of predetermined magnitude applied between the control electrode and the principal electrodes thereof.

More concisely stated, it is an object of my invention to provide a power amplification relay of the type that shall have two regions of operation,

,- one region wherein its amplification factor shall have a series of low values and another region in which its amplification factor shall have a series of high values, and that shall be capable of abrupt transition from one region to the other by impulse actuations of a predetermined magnitude.

According to my invention, I provide a relay system of the type incorporating an electric discharge device having a plurality of principal electrodes, the current output of which, when expressed as a function of the potential impressed between the principal electrodes, has at least one maximum point and one minimum point. Mathematically, such a function may be readily described by saying that it might be represented by an algebraic expression of at least the third degree.

It is to be noted that an algebraic function of the third degree in general, has three roots and may, therefore, have three intersections with a straight line.

tion exponentiais or in circular, hyperbolic or elliptic functions might also satisfy the requirem nt of having at least two stationary points.

My invention is of course, not to be restricted in any manner as regards the particular type of expression whereby the current transmitted between the principal electrodes of the electric discharge device is represented as a function of the potential imressed therebetween.

The function whereby the current transmitted between the principal electrodes of the device is expressed in terms of the potential is not, in general, a simple function that may be represented by a single curve. The function is more adequately determined by a family of curves the parameter or parameters of which relate to the other properties of the electric discharge device. For example, if the electric discharge device incorporates a control electrode, the parameter of the above discussed family of functions is itself a function of the potentials impressed between the prin ipal electrodes and the control electrode.

While the control potential represents one parameter whereby the particular function of a family that may be selected, it is not the only property of the electric discharge device that may determine its operation. For example, the temperature at which the electric discharge device as is often the casein mathematical treatises,

is operating at any particular time and the other elements of the circuit in which the electric discharge device is connected might also be parameters in accordance with which a particular function of a family of functions may be selected. As shall be seen hereinafter, my invention has been particularly applied to a system in which the control potential is the determining parameter. However, while this particular system has a number of advantageous features, it is important to bear in mind that I do not intend that my invention shall be restricted to such a system.

In accordance with the practice of my invention, an impedance is connected in series With the principal electrodes of the electric discharge device. This impedance is of such magnitude and character that the current transmitted therethrough, when expressed as a function of the potential impressed thereacross, may be represented by a curve that intersects one curve of the family of curves, representingthe functions whereby the current transrnitted between the principal electrodes is expressed as a function of the potential between the electrodes, at at least three points. It will be noted that since the current transmitted through th impedance and the current transmitted between the principal electrodes is the same, the three points of intersection are representative of three possible regions of operation of the electric discharge device. One of these regions is, in general, a region oi unstable operation, while the other two regions are regions of stable operation. The point which represents the actual condition of the electric discharge device is determined by the past history of the electric discharge device.

Among the family of curves which represent the current transmitted between the electrodes of the electric discharge device as a function of the principal potential, there are a class which are intersected by the impedance curve at only one point. This class of curves may be subdivided into two groups. For one group of the curves the intersection occurs on one side of the two stationary points while for the other group of curves the intersection occurs on the other side of the stationary points. if the condition of operation of the electric discharge device should be such as to be re resented by a curve which is intersected by the impedance curve at three points, the point of intersection representing the actual condition of operation is determined by which of these two groups of curves represented the actual operation of the electric discharge device immediately before its operation changed so as to be represented by the curve intersected at three points. It is seen that if the actual operation was represented at the prior time by one of one group of the singly intersected curves, the point of intersection representing the operation after the transition to the triply intersected curve is a point that is on the same side of the stationary points as are the single intersection points of the impedance curve and this group of curves. On the other hand, if the p or operation was represented by the other group of singly intersected curves the point of intersection is determined in a similar manner.

As a result of this property of the system, it is apparent that the output of the electric discharge device will be represented by two overlapping regions of points corresponding to the points of intersection of the impedance curve and family of curves of the electric discharge devices. The transition from one region of points to the other can only take place if the particular property representing the parameter of the electric discharge device is so changed that the actual condition of operation of the device is varied from one region of singly intersected curves to another. In the system in which my invention has been specifically embodied the change from one group of curves to another is produced by an impulse of predetermined magnitude impressed on the control electrode of the electric discharge device.

The novel features that I consider characteristic of my invention are set forth with particu larity in the appended claims. The invention itself, however, both as to its organization and its iethod of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment, when read in connection with the accompanying drawing, in which Figure 1 is a graph showing the characteristics oftne electric discharge devices utilized in the practice of my invention, and

Fig. '2 is a diagrammatic View showing an embodiment of my invention.

In the graph shown in Fig. 1 the current transmitted between the anode 1 and the cathode 3 of an electric discharge device 5 of the type incorporating a screen grid 7 (such as is shown in Fig. 2 for example) is plotted as a function of the anode-cathode potential. The plot comprises a family of curves 9, 11, 13, 15 and 17, each curve being independent of the others, and being dependent upon the particular potential that is impressed on the control electrode 19 of the electric discharge device 5. For the particular type of electric discharge device 5'utilized the uppermost curvel'? corresponds to a potential of zero impressed between'the control electrode 19 and the cathode 3 while the lowermost curve 9 corresponds to a control potential of 4.5 volts impressed between the control electrode 19 and the cathode 5. The intermediate curves 11, 13 and 15 represent corresponding intermediate conditions.

The curves 9, 11, 13, 15 and 17 shown are plotted from the results of measurements taken with a radiotron tube type UX-222. As will be noted, each curve has one maximum point 21, 23, 25, 27

. and 29 and one minimum point 31, 33, 35, 37 and 39. It is to be noted that the property shown by the curves is, in general, common to all screen grid electric discharge devices and to other devices particularly those of the gas-filled type. I have found that the same characteristics as are shown in Fig. 1 can be attained with the W estinghouse industrial tube DRJ-571. This tube is a pentode, but if the potentials impressed upon the various electrodes are properly adjusted, the desired characteristic is attained.

The current which is transmitted through a resistor 41 (Fig. 2) connected in series with the anode 1 and the cathode 3 of the electric discharge device 5 is also plotted in Fig. 1 as a function of the potential impressed across the terminals of the resistor. [is will be noted, this curve is a straight line 43 which intersects one of the anode-cathode curves 13 (i. e., the one corresponding to a control potential'of 1.5 volts), at three points 45, 4'7 and 49. The straight line 43 is also tangent to the anode-cathode curve 15 corre sponding to a control potential of 1 voltage and also to the curve 11 corresponding to a potential v1 of 3 volts. The latter curves 11 and 15 and each of the remaining curves 9 and 1'7 are each intersected by the straight line 43 at a single point 51, 53' and 55. Since the curves 15 and 17 are sub stantially coincident near the origin, the straight line 43 intersects them both at the same point 53.

ince the current transmitted between the anode 1 and the cathode 3 of the electric discharge device 5 is equal to the current transmitted through the resistor 41, the points of in- .u

tersection of the straight line 43 and the anodecathode curves 9, 11, 13, 15 and 17 represent possible conditions of operationof the electric dis charge device.

Consider first the curve 13 that is intersected at three points 45, 4 7 and 49 by the straight line 43. At the two terminal points of intersection 45 and 419 the slope of the curve 13 is such that the anode-cathode current is an increasing function of the anode-cathode potential. These points, therefore, represent possible stable conditions of the electric discharge device 5. In the region of the central point of intersection 47 of the straight line 43 and the curve 13, however, the anodewathode current is a decreasing function of the anode-cathode potential and the operation of the electric discharge device 5 is, therefore, unstable at this point. The two points which, general, represent actual possible conditions of the electric discharge device are the two terminal stable points 45 and 49 and the other point 47 merely represents a condition which could only occur under very particular circumstances rarely encountered. The essence of my invention resides in the fact that the particular one of these two st ble poi i5 and 49 which represents an actual condition or the electric discharge device 5 at any time is predetermined by the immediate prior history of the electric discharge device.

If it now assumed that the control potential on the electric discharge device 5 is so adjusted that condition of operation is represented by the lower curve 9, the current output of. the electric discharge device is represented by the point of in r ection of this curve and the straight line to be noted that in this case only one condition is possible.

if the control potential is then increased until the operation of the electric discharge device 5 is represented by the curve 11 directly above the lowest curve, the graphic representation is reduced to a system in which the strai ht line 43 intersects the curve 11 at one point 51 and is tan ent to it at another point 57. However, the actual condition of operation of the electric discharge device 5 is represented by the point of intersection 51 not by the point of tangency by reason of continuous transition which must necessarily take place as th indication of the electric discharge device varies from that represented by the point 55 to that represented by the point 51.

As the control potential is now further increased a condition of the electric discharge device 5 will eventually be obtained which is represented by the curve 13 that is intersected by the straight line 43 at three points. The actual operation of the electric discharge device will then be represented by the point of intersection that is most adjacent to the region in which the operation has been heretofore and consequently will be represented by the point of intersection 45 of the curve 13 and the straight line 43 that is on the extreme right.

(in still further increase of the control potential, a condition of the electric discharge device 5 is attained which is represented by the second curve 15 from the top. This curve is tangent to the straight line 43 at one point 59 on the right and intersects the straight line at the point 53 on the left. As has been seen heretofore, the dition of operation of the electric discharge ice will at this time be represented by the point of tangency 59 of the straight line 43 and the curve 15. I

As is apparent in the plot shown in Fig. 1 distinct conditions of the electric discharge device 5 are represented. Conditions intermediate between these distinct conditions will be represented by curves intermediate the curves shown. Of

these curves all of the curves above the last mentioned curve 15 will intersect the straight line 43 in only one point and this point will be in the region of the extreme left of the drawing. It is seen, therefore, that if the control potential is further increased the actual condition of operation of the electric dischar e device 5 necessarily be represented by a point in the region oi the point of intersection 53 of the secon curve 15 from the top and the straight line If the control potential is increased to such a value that the topmost curve 1? represents the condition or" the electric discharge device 5, the condition of operation of the device is still represented by the point of intersection 53 of the topmost curve and the straight line 43.

It is seen that when this condition is attained the operation of the electric discharge device 5 is entirely in a difierent region from its prior condition of operation. If the control potential is now decreased, within the limits determined by the lower curve 11 to whi h the straight line i3 is tangent, the condition of operation of the electric discharge device 5 will remain in the region of the intersection 53 of the straight line 43 with topmost curve 17. The electric discharge device 5 will, therefore, operate differently than it did before for the same control potentials as were impressed thereon. The only manner in which th condition of the electric discharge device may be reverted to its ori inal character is by so var ing the control potential as to cause it to operate in a region represented by a curve below the lower curve 11 to which the straight line 43 is tangent.

For the particular electric discharge device 5 from which Fig. 1 was plotted, it is seen that n the control electrode 19 has a potential of zero impressed thereon, the condition of operation is relegated to the region of the single point 53 of intersection of the topmost curve 17 and straight line 3. The character of the output of the electric discharge device 5 is not materially changed-as long as the potential impressed on the control electrode 19 is not decreased beyond -3 volts. However, if a decrease greate than -13 volts occurs the operation of the electric discharge 5 is shiitecl to the right hand region and now its condition is represented by the points of intersection or tangency -15, 51, 55 and 59 of the curves 13, 11, 9 and 15 and the straight line as that are on the extreme left. In this region the control potential. may be varied from 1 volt to -45 volts without causing any abrupt change. It is to be noted that the variation in the potential impressed across the elec 'ic discharge device 5 which is produced by the abrupt change is from a value of the order of 5 volts to a value of between 35 and 4c volts. It can be seen that this corn-- paratively large change of potential can be utilized'with considerable advantage in power plifying systems.

In Fig. 2 a system embodying my invention is shown. The essential element in this system is the discharge device 5 which incorporates the anode 1, the cathode 8, the screening electrode 7 and the control electrode 19. A suitable device of this type is the radio-tron UX-222 or the Westinghouse industrial tube DRJ-57l. However, any number of other devices of the same type are available and may be utilized if the necessity therefor arises.

The potential impressed between the control. electrode 19 and the cathode 3 of the electric discharge device 5 is varied by an ordinary three electrode electric discharge device 61, the anode 63 of which is connected to the control electrode 7 of the screen grid electric discharge device .5 through an impedance 65 and the cathode 67 of which is connected to the cathode 3 of the screen grid electric discharge device. The current transmitted between the anode 63 and the oathode 67 of the three electrode electric discharge a device 61 is varied by an impulse receiver such as a photo-sensitive device 69, for example. The anode 71 of the photo-sensitive device 69 is connected to the anode 63 or" the three electrode electric discharge device 61 through a resistor 73 and the cathode 75 of the photo-sensitive device is connected to the control electrode 77 of the electric discharge device 61 through an impedance '79.

It is to be noted that as shown in the drawing the impedances 65 and 79 are capacitors. However, by using the word impedance to describe them hereinabove, I meant to infer that any type of impedance might be utilized. The operation of the system will depend upon the particular type impedances 65 and 79 that are utilized. In general, however, two distinct conditions of operation are possible. 7

1'. Where the impedances 65 and 79 are resistors and 2. Where these impedances are capacitors.

I shall first discuss the case in which the impedances are resistors. In such a case it is generally desirable to connect a source of potential in series with the impedances 65 and 79 to maintain. the control electrodes 19 and 77 of the electric discharge devices 5 and 61 properly biased.

As the illumination impinging on the photo-, sensitive device 69 is varied, the current output of the three electrode electric discharge device 61 is varied and the control potential of the screen grid electric discharge device 5 is varied. The variation of control potential impressed on the screen grid electric discharge device 5 produces changes in the characteristics of the electric discharge device which may be graphically, represented by shifts from one curve to another of the family of curves 9, l1, 13, 15 and 17 shown in Fig. 1. As has been explained hereinabove, the resistor 41 is connected in series with the anode 1 of the screen grid electric discharge device 5 and is of such magnitude that the curve 43 representing the current transmitted therethrough as a function of the potential impressed across its terminals intersects certain of the curves representing the characteristic of the screen grid electric discharge device 5 at three points as is shown in Fig. 1.

The screen grid electric discharge device 5 is utilized for the purpose of triggering ofi a gasfilled electric discharge device 81 such as the Westinghouse industrial tube KU-627 or KU-628 for example. For this reason its principal electrodes 1 and 3 are connected between the control electrode 83 and the cathode 85 of the gas-filled electric discharge device 81. The anode 1 of the screen grid electric discharge device 5 is connected to the control electrode 83 of the gas-filled electric discharge device 81 through a suitable resistor 87 while its cathode 3 is connected to the cathode 85 of the gas-filled electric discharge device 81 through a suitable potentiometer 89. The specific features of the circuit do not concern the present invention and need not be discussed herein.

As the radiations impinging on the photosensitive device 69 are varied, the region of opv 9 of Fig. 1.

eration of the electric discharge device 5 is varied. For variations in the flux of the radiations of certain magnitudes ,no change in the region ofoperation of the electric discharge device 5 is produced and substantially no change in the condition of operation of the gas-filled electric discharge device is produced. However, if the variation of radiation flux impinging on the photo-sensitive device 69 attains a predetermined value, an abrupt change in the region of operation of the screen grid electric discharge device 5 takes place and a corresponding abrupt change in the condition of operation of the gasfilled electric discharge device 81 takes place.

Let it be assumed for the purpose of explanation that the photo-sensitive device 69 is highly illuminated. Keeping in mind that in the system under discussion here the impedances 65 and 79 are resistors, it will be seen that the control electrode 77 of the three electrode electric discharge'device 61 is charged positive and the impedance of this electric discharge device is low. The difference of potential between the control electrode 19 and the cathode 3 is therefore comparatively low. The screen grid electric discharge device 5 is, therefore, in a condition which is represented by a curve such as the lowermost anode-cathode curve The drop in potential in the'plate circuit of the screen grid electric discharge device 5 isgreat and the gas-filled electric discharge device 81 is energized.

If the illumination impinging on the photosensitive device is now varied in'such manner that the control potential impressed on the screengrid electric discharge device 5 does not result in a change of characteristic of the electric discharge device which would be represented by a curve above the upper curve 15 to which the straight line 43 is tangent, the gas-filled electric discharge device 81 remains in energized condition.

However, if a decrease in the illumination occurs which is of such magnitude that the operation of the screen grid electric discharge device 5 is changed to a condition for example represented by'the upper curve 17 of the family of curves shown in Fig. 1, the condition of the screen grid electric discharge device 5 is abruptly changed and the potential impressed between its principal electrodes 1 and 3 is considerably decreased. By

reason of the decrease in potential, the gas-filled electric discharge device 81 is de nergized as soon. as its principal potential is reduced to a low enough value. It remains in its deenergized condition until the illumination impinging on the photosensitive device. 69 is increased to such a value as would result in a characteristic anodepotential curve below the lower curve 11 tangent to the straight line 43 in Fig. l.

Now I shall consider the case in which the impedances 65 and 79 are capacitors. This case corresponds with the actual symbolica-l representa-- tion of Fig. 2. In this system the control electrode 19 of the screen grid electric discharge device 5 has impressed thereon a potential from a potentiometer 91 through a resistor 93 that is of such magnitude that the electric discharge device 5 normally operates in a manner represented by the central curve 13 or" Fig.1. That is to say the operation of the electric discharge device is under normal conditions in a region such that the representative curve is intersected at at least three points by the impedance curve 43.

The three points at which the line 43 intersects the curve 13 represent three possible conditions of operation of the electric discharge device 5. The

point representing the actual condition of operation thereof will depend upon the polarity of the impulse to which it is desirable that the system shall respond. If it is desired that the point of operation be the point of intersection 49 on the left, the movable contactor 95 of the switch 9'7 is brought into engagement with a fixed contact 99 connected to the cathode 3 of the eletric di"- charge device 5 and then reverted to engagement with the fixed contact 191 that is connected to the movable tap 103 of the potentiometer 9i. is desired that the electric discharge device 5 -a normally operate in a region correspondii the point of intersection 45 in the right the movable contactor 9-5 is brought into engagement with a fixed contact 105 connected to the most negative terminal 107 of the potentiometer 91 and then reverted to engagement with the central contact 101.

The particular region in which the operation of the electric discharge device is normally maintained is dependent on the polarity of the impulse to which it is desired that the system shall respond. Let it be assumed that it is desired that the system shall respond to impulsive decrease the radiant flux inging on the photo-sensi tivc device. The movable tap 193 of the potentiome er 91 is first adjusted to such a point that the control potential of the electric discharge device 5 is of the order or" 1.5 volts. The movable contact-or 95 of the switch 9'? is then brought into engagement with the lower contact 95 which is connected to the lower terminal 107 of the potentiorneter 91, the latter at a potential of the order of 1.5 volts. The movable contactor 95 is then reverted to engagement with the central fixed contact 191 and the system is in a condition for operation with the screen grid electric discharge device 5 in a condition represented by the right point of intersection .5 of the central curve 13 and the straight 43 of Fig. 1. It to be noted that for this condi the difference in potential between the control c ectrode 83 and the cathode 85 of the gas-r led electric discharge device 81 is high and the electric discharge device is energized.

Since the photo-sensitive device 69 is connected to the control electrode 77 of the three electrode electric discharge device 61 through a capacitor '79 and since the plate circuit of the three electrode electric discharge device 61 is connected to the control electrode 19 of the screen grid electric discharge device 5 in a similarmanner the system does not respond to slow variations of the radiant energy impinging on the cathode '75 of the photo-sensitive device 69. However when an impulsive decrease of the impinging radiant flux occurs, the drop in potential across the photo-sensitive device 69 is suddenly increased and there a sudden rush of current through the resistor 199 through which the capacitor 79 and the control electrode of the three electrode electric discharge device 61 are connected to the lower tap 107 of the potentiometer 91.

The direction or the flow of current is from the lower tap 107 to the control electrode '77 and the drop in potential is therefore of such polarity as to decrease the potential of the control electrode '77 relative to the cathode 67. A sudden decrease in the current output of the three electrode electric discharge device 61 therefore occurs and the drop in potential across the resister in series therewith is suddenly decreased.

For this reason an impulsive current flows through the resistor 93 that is connected to the control electrode 19 or" the screen grid electric discharge device 5. This current is in a direction away from the control electrode and potential of the control electrode 19 is suddenly increased relative to the cathode 3. If the impulse is of high enough magnitude the condition of operation or" the electric discharge de' ce 5 will suddenly be shifted to a region represented by a curve above the upper curve tangent to the straight line 13; the operation of the elec- "3 discharge device 5 will now be represented by the point 53 and when the impulse is disccntinued and the photo-sensitive device 69 reverted to its intlal condition the screen grid electric disch: e device 5 will operate in a region repre.-entcd c; the left hand point of intersection 19 of the cen l curve 13 and the straight line 43. When the screen grid electric discharge device 5 in this condition the gas filled electric discharge device 81 is deenergized and load 111 energized therefrom is correspondingly affected.

When it is desired that the system be again rendered responsive to an impulsive decrease in the flux impinging in the photo-sensitive device 69 the movable contactor 95 of the switch 9'? may again be brought into contact with the lower contact 105 and then reverted to its initial condition. If the system is left in the condition to which the above decreasing impulse reverted, it is responsive only to an impulsive increase of the flux impinging on the photo-sensitive device 69. The manner of its response in this connection is similar to its manner of response to an impulsive decrease in the radiant flux and an explanation of the operation similar to that given hereinabove may be applied in this case. By the impulsive increase in the radiant flux impinging on the photo-sensitive device 69 the drop in potential across the photo-sensitive device is decreased, the impulsive current flowing through the resistor 109 is in the direction away from the associated control electrode 7'7, the current output of the three electrode electric discharge device 61 is therefore increased, the drop in potential across the resistor 73 connected in series therewith is increased, the impulsive current flowing through the resistor 93 is towards the associated control electrode 19, the screen grid electric discharge device 5 is reverted to a condition represented by the left hand point of intersection and the gas filled electric discharge device 81 is energized.

If it is desired that the system shall respond to alternative impulses of positive and negative polarity impinging on the photo-sensitive device 69 the switch 9'7 need not be utilized. However, if it is desired that the system shall respond to impulses of only one polarity, the movable contactor 95 of the switch 97 must be reverted afe every actuation of the system either to the lower fixed contact 165, if the system is to respond to decreasing radiant energy impulses, or to the upper contact 99, if it is to respond to increasing radiant energy impulses.

Ihe switch 97 shown in Fig. 2 is only to be particularly useful in the present invention is one comprising a plurality of insulating discs, each disc having a plurality of conducting segments disposed therein and a plurality of brushes to coact with the segments. The discs may be mounted in a single shaft and segments on one disc may be connected to the lower or upper terminal of the potentiometer 91, depending upon the particular type of operation of the system that is desired, while the segments on the other disc may be connected to the movable tap 103 of the potentiometer 91. The control electrode 19 of the screen grid electric discharge device 5 may be connected to each disc in such manner that when a segment in any particular disc is in contact with a point on the potentiometer the control electrode is at the corresponding potential.

The discs may be so oriented on their shaft that the segments overlap and the control electrode l9 consequently is prevented from floating. The relative lengths of the segments may be so adjusted and the discs may be rotated at such a rate as to provide for the detection of impulses at any desired rate.

It will be apparent from a consideration of the above discussion that my invention may be applied with considerable advantage in a number of situations. In particular it has applicability in equipment utilized for sorting articles by photo-sensitive means and one of its principal uses is in the field of tin plate sorting. In this connection particular attention is called to a copending application, Serial No. 574,338 filed Nov. 11, 1931 to Clinton R. Hanna and E. Forrest Critchlow and assigned to the Westinghouse Electric and Manufacturing Company. In this application a system for sorting tin plates is shown. My invention may be applied with advantage in this system, and may replace the amplilier system shown.

As will be apparent from a consideration of the above dis ussion the last described modification of my invention ispreferablefor tin plate sorting to the first described embodiment; However, in either of. the systems, the lock-in feature is valuable sinc it may be utilized to eliminate the difficulties which arise from the fact that the tin plates sorted are often spotted from causes which do not render them objectionable and unless a system such as is shown in the present connection is utilized, the amplifier responds to spots of this type as well as to spots arising from objectionable causes. Since the non-objectionable spots arise from such causes as finger prints are generally not so optically different from the normal plates as are the objectionable spots, my invention may be utilized in these systems to discriminate between iobjectionable spots and non-objectionable ones.

Finally it is well to keep in mind that the photo-sensitive device is not the only detecting element which is usable in the practice of my invention. The photo-sensitive device is responsive to radiant energy. A thermocouple might be utilized to respond to changes in temperature; a humidity responsive device, such as a hygroscopic material, might be utilized to detect sudden changes in humidity; a microphone might be utilized to respond to sudden sound impulses; a tuned circuit might be utilized to respond to incoming wave impulses or other detecting devices of suitable type might be utilized to respond to corresponding changes in the properties of a particular region under observation. It is interesting to note that a temperature responsive device replaces the photo-sensitive device 69, the load 111 may be a heater element which changes the temperature of the region under observation in response to the variations produced by the temperature responsive device, and so also the load may be a humidity varying vice being of the type wherein the current between at least two of said electrodes may be represented by a family of at least third degree functions of the potential impressed therebetween, an impedance connected in such manner with regard to said last mentioned two electrodes that the current transmitted between said electrodes is transmitted through said impedance, means for impressing a direct current po tential across said impedance and said lastnamed electrodes, said impedance and said potential being of magnitudes such that the curve representing the current transmitted through said impedance as a function of the potential impressed between said last-named electrodes intersects at least one of the family of curves representing the current transmitted between said last named two electrodes as a function of potential at at least three points, and means for determining that particular function of said family of functions which represents the actual condition of operation of the discharge between the electrodes so that the operation of said electric discharge device is limited to but a single region.

2. In combination an electric discharge device incorporating a plurality of electrodes, said device being of the type wherein the current between at least two of said electrodes may be represented by a family of at least third degree func tions of the potential impressed therebetween, a resistor connected in such manner with regard to said last mentioned two electrodes that the current transmitted between said electrodes is translast named electrodes as a function of potential at at least three points, and means for determining that particular function of said family of functions which represents the actual condition of the discharge between the electrodes so that the operation of said electric discharge device is limited to but a single region of said points of intersection.

3. In combination an electric discharge device l incorporating a plurality of electrodes, said delvice being of the type wherein the current between at least two of said electrodes may be represented by a family of at least third degree functions of the potential impressed therebetween, an impedance connected in such manner with regard to said last mentioned two electrodes that the current transmitted between said electrodes is transmitted through said impedance, -means for impressing a direct current potential across said impedance and said last-named electrode, said impedance and potential having properties such that the curve representing the current transmitted through said impedance as a es as a function of potential at at least three ts, and means for determining a particular function of said family of functions which represents the actual condition of the discharge beelectu discharge device is limited to but a sin- 15 gle le ion.

In combination an electric discharge device incorporating a plurality of electrodes, said device being of the type wherein the current between at least two of said electrodes maybe represented by a far -ily least third degree functions of the potential impressed therebetween, an impedance connected in such m inner with regard to said last mentioned two electrodes that the current transmitted between electrodes is transmitted through said impedance, means for impressing direct cu rent potential across said impedance and last-maimed electrodes, said impedance and potential being of magnitudes such that the curve representing the current transmitted ough impedance as a function of the posed between said last-named elec- :rChfi-lgE device and one of esentative of an unstable ic discharge device, and for determining a particular function of functions which represents the acondition of the discharge between the elecdes so that the operation of said electric dison ion A n x dpelsas t g a to but a single region. Q 5, In combination, an electric discharge device incorpor .g control electrode and a plurality r or pr,

electrodes, said device being of the type wherein the current transmitted between saic principal ele trodes nny be represented by a farm- JI' ily of functions of the character that have at least station uy points of the potential impressed ectrodes, the parameter of said function of the potentials inie rcipal electrodes; impedance so connected I electrodes that the current transted be en said electrodes is transmitted hrcugh im dance, means for impressing a t current po icil across i ioedance and aid or icipal eiee said impedance and said .roperties su h that the curve tne current temitted through a function 0. the potential al electrodes inter- J the current transmitted between said ctrodes as a function of the potential ereoetween at least three points,

or con pilin the potential impressed conti cl electrode and said principal select motion of said .t the current .itted between prncipal electrodes to csent the actual of the discharge tween said principal electrodes and thereby to localize the operation of said electric discharge device in a region represented by one or" said points of intersection.

6. In combination, an electric discharge device incorporating a control electrode and a plurality of principal electrodes, said device being of the type wherein the current transmitted between p incipal electrodes may be represented by a family of functions of the character that have at least two stationary points of the potential impressed between said electrodes, parameter of said functions Y a function of the potentials impressed between said control electrode and said principal electrodes; an impedance so connected to said rincipal electrodes that the current transmitted bet een said electrodes is transmitted through said impedance, means for impressing a direct current potential across impedance and said principal electrodes, said impedance and said potential having properties such that the curve representing the current transmitted through said impedance as a fraction of t e potential impressed between said principal electrodes intersects at least one curve of the family of curves repres-en g the current transmitted between said principal electrodes as a function of the potential impressed therebetween. at at least three points and means for controlling the potential impressed between said control electrode and said principal electrodes to select a particular function of said family of functions that represent the current transmitted between said principal electrodes to r 'esent the actual condition of the discharge be een said principal electrodes, said function being of such character that the curve representing it is intersected only at one point by the cure repre senting the current transmitted through said irnpedance and thereby to localize the operation of said electric discharge device in a region represented by one or" said above recited three points or" intersection.

'7. In combination an electric discharg de" ice incorporating a plurality of electrod vice being of a type wherein the u at least two of said electrodes may a sented by a family of at least third degr e tions of the potential impressed therebet an impedance connected in such manner t regard to said last mentioned two eec rodes m that the current transmitted between said electrodes is transmitted through said impedance, means for impressing a direct current potential across said impedance and last-named electrc es, said impedance and said potential being of magnitudes such that the curve representing the current transmitted through said impedance as a function or" the potential imp-c etween said. last-named electrodes intersects least one of the family of curves representing the current 5 transmitted between said last named two electrodes as a function of potential at at least three points and means for determining a particular function of said family of functions to represent ill) the electrodes, said function being of a character such that the curve representing it is intersected at one point only by the curve rep-res .ig the current transmi ted through said thereby to localize the operation of discharge device in he region repres nt of said above recited three points of electrode, said device being of the type wherein Lg? the current transmitted between said anode and cathode may be represented. by a family of functions of the character that have at least two stationary points, of the potential impressed between said anode and said cathode, the parameter of said family of functions being a function of the potentials impressed between said control electrode and said anode and cathode; an impedance so connected to said anode and cathode that the current transmitted between said anode and cathode is transmitted therethrough, means for impressing a direct current potential across said impedance and said anode and cathode, said impedance being of a character such that the curve representing the current transmitted through said impedance as a function of the potential impressed between said anode and cathode intersects at least one of the curves of said family of curves representing the current transmitted between said anode and cathode as a function of the potential impressed therebetween at at least three points and means for controlling the potentials impressed between said control electrode and said anode and cathode to select a particular function of said family of functions that represent the ciurent transmitted between said anode and cathode to represent the actual condition of the discharge between said anode and cathode, said function being of a character such that the curve representing the current transmitted through said impedance intersects the curve representing said function at one point only, thereby to localize the operation of said electric discharge device in the region of one of said above recited three points of intersection. Y

9. In combination an electric discharge device having an anode, a cathode, a control electrode and a screening electrode between said control electrode and said anode, said device being of the type wherein the current transmitted between said anode and cathode may be represented by a family of functions of the character that have at least two stationary points, of the potential impressed between said anode and said cathode, the parameter of said family of functions being a function of the potentials impressed between said control electrode and said anode and cathode; an impedance so connected to said anode and cathode that the current transmitted between said anode and cathode is transmitted therethrough, means for impressing a direct current potential across said impedance and said anode and cathode, said impedance and said potential being of a character such that the curve representing the current transmitted through said impedance as a function of the potential impressed between said anode and cathode intersects at least one of the curves of said family of curves representing the current transmitted between said anode and cathode as a function of the potential impressed therebetween at at least three points and means for controlling the potential impressed between said control electrode and said anode and cathode to select a particular function of said family of functions that represent the current transmitted between said anode and cathode to represent the actual condition of the discharge between said anode and cathode, said functions being of a character such that the curve representing the current transmitted through said impedance intersects the curve representing function at one point only, thereby to localize the operation of said electric discharge device in the region of one of said above recited three points of intersection.

10. A lock-in relay comprising a thermionic device of the type incorporating a screen grid, a control grid, and a plurality of principal electrodes, a resistor connected "'3 series with said principal electrodes and a direct current potential connected across said resistor and said principal electrodes, said resistor and potential being of magnitudes such that the curve representing the current transmitted through said resistor as a function of the potential impressed between said principal electrodes intersects one of the family of curves representing the cu rent trans mitted between said principal electrodes as a function of the potential impressed therebetween at at least three points and means for impressing potentials between said control electrode and said principal electrodes to localize the operation of said thermionic device in the region of one of said points of intersection.

11. An impulse responsive lock in system comprising an electric discharge device having a plurality of electrodes, said device being of the type wherein the current between at least two of said electrodes may be represented by a family of at least third degree functions of the potential impressed therebetween, an impedance connected in such manner with regard to said last-mentioned two electrodes that the current transmitted between said electrodes is transmitted through said impedance, means for impressing a direct current potential across said impedance and said last-named electrodes, said impedance and said potential having properties such that the curve representing the current transmitted through said impedance as a function of the potential impressed across its terminals intersects at least one of the family of curves representing the current transmitted through said last named three electrodes as a function of potential at at least three points, means for maintaining said electric discharge device in a condition such that the current between said above mentioned two electrodes is represented by a curve intersected at three points by said impedance curve, means for localizing the operation of said electric discharge device in a region of one of the points of intersection and means, for detecting an impulse of a physical disturbance, coupled to said electric discharge device for varying its condition of operation and localizing it in the region of another point of intersection.

12. An impulse responsive lock in system comprising an electric discharge device having a plurality of electrodes, said device being of the type wherein the current between at least two of said electrodes may be represented by a family of at least third degree functions of the potential impressed therebetween, an impedance connected in such manner with regard to said last-mentioned two electrodes that the current transmitted between said electrodes is transmitted through said impedance, means for impressing a direct current potential across said impedance and said lastmentioned electrodes, said impedance and said potential having properties such that the curve '3 representing the current transmitted through said impedance as a function of the potential impressed between said last electrode intersects at least one of the family of curves representing the current transmitted through said last named three electrodes as a function of potential at at least three points, means for maintaining said electric discharge device in a condition such that the current between said above mentioned two electrodes is represented by a curve intersected at three points by said impedance curve, means for localizing the operation of said electric discharge device in a region of one of the points of intersection and means, for detecting an impulsive variation of radiant energy, coupled to said electric discharge device for varying its condition of operation and localizing it in the region of another point of intersection.

13. In combination, an electric discharge device incorporating a control electrode and a plurality of principal electrodes, said device being of the type wherein the current transmitted between said principal electrodes may be represented by a family of functions of the character that have at least two stationary points of the potential impressed between said electrodes, the parameter of said functions being a function of the potentials impressed between said control electrodes and said principal electrodes; an impedance so connected to said principal electrodes that the current transmitted between said electrodes is transmitted through said impedance, means for impressing a direct current potential across said impedance and said principal electrodes, said impedance and said potential having properties such that the curve representing the current transmitted through said impedance as a function of the potential impressed between said principal electrodes intersects at least one curve of the family of curves representing the current transmitted between said principal electrodes as a function of the potential impressed therebetween at at least three points, means for impressing potential between said control electrode and said principal electrodes to maintain said electric discharge device in a condition represented by one of said electric discharge device curves intersected at three points by said impedance curve, means for impressing potentials between said control electrode and said principal electrodes to localize the operation of said electric discharge device at one of said points of intersection and means to respond to an energy impulse to vary the condition of operation of said electric discharge device and to shift it to a region represented by another of said points of intersection.

14. In combination, an electric discharge device incorporating a control electrode and a plurality of principal electrodes, said device being of the type wherein the current transmitted between said principal electrodes may be represented by a family of functions of the character that have at least two stationary points of the potential impressed between said electrodes, the parameter of said functions being a function of the potentials impressed between said control electrode and said principal electrodes; an impedance so connected to said principal electrodes that the current transmitted between said electrodes is transmitted through said impedance, means for impressing a direct current potential across said impedance and said principal electrodes, said impedance having properties such that the curve representing the current transmitted through said impedance as a function of the potential impressed between said principal electrodes intersects at least one curve of the family of curves representing the current transmitted between said principal electrodes as a function of the potential impressed therebetween at at least three points, means for impressing potential between said control electrode and said principal electrodes to maintain said electric discharge device in a condition represented by one of said electric discharge device curves intersected at three points by said impedance curve, means for impressing potentials between said control electrode and said principal electrodes to localize the operation of said electric discharge device at one of said points of intersection and means to respond to a radiant energy impulse to vary the condition of operation of said electric discharge device and to shift it to a region represented by another of said points of intersection.

THOMAS H. LONG. 

